1. Field of the Invention
The present invention relates to an insulation type switching power supply apparatus.
2. Description of Related Art
Generally, an insulation type switching power supply apparatus has a structure in which an auxiliary winding and a photo-coupler are used to perform feedback control of an output voltage (see FIG. 9 and FIG. 10).
Besides, insulation type switching power supply apparatuses, which perform feedback control of an output voltage without using an auxiliary winding and a photo-coupler, are also proposed (U.S. Pat. No. 7,463,497 and U.S. Pat. No. 7,471,522) (hereinafter, called patent documents 1 and 2).
However, in a first conventional example (FIG. 9) that uses an auxiliary winding, there are problems of a needed custom transformer, board area increase, and cost increase. Besides, in a second conventional example (FIG. 10), there are problems of consumed electric current increase (efficiency deterioration), long-term reliability decline, board area increase, and cost increase.
Besides, the conventional techniques of the patent document 1 and patent document 2 need an error amplifier, a sample/hold circuit and the like, and have room for further improvement as to circuit scale reduction.